Westminster insiders say the Altmann’s decision to criticise the Treasury’s proposal to tax pensions in the same way as Isas puts her on a collision course with the Chancellor.

And a move to tax contributions, rather than withdrawals, in the March Budget would leave Altmann with the choice of either departing office or performing a humiliating U-turn and backing a policy she has publicly denounced.

One source says: “If George Osborne decides he is going to flip the pensions tax regime on its head, I don’t think Ros Altmann will stay in Government. She has been so clear about her opposition to it that I don’t believe she can stay.”

Another adds: “Given that the Chancellor may be looking to make much wider reforms to tax relief at Budget, he will want people on board who are going to help carry that message forward.

“You can’t have a situation where a minister in charge of a portfolio like pensions is repeatedly at odds with the main department leading on it.”

And it’s not just the Government’s pensions policy the minister has slighted.

Indeed, it remains unclear how comfortable Altmann feels operating within the rules of a manicured and polished Government, as opposed to pushing against it, as she did with such success in a past life.

In early December Altmann retweeted another message, this time from Hargreaves Lansdown’s Tom McPhail, who made reference to opposition minister Nick Thomas-Symonds claiming Altmann “seems to have been able to exercise more influence outside Government than in”.

Then there was the email Altmann sent to journalists just before Christmas, in which she said: “…my life seems to have turned upside down but hopefully things will settle back down again soon.”

She added: “I haven’t been able to speak to people much and am not in control of my diary”.

And battles like that over women’s state pensions will be further sapping the minister’s energy.

Altmann fought hard while outside Government to improve the situation for women of the 1950s, who have seen their retirement age climb from 60 to 66.

One industry source with close ties to the minister says: “It is a very hard journey to go from being a very good lobbyist to being a minister of state. The two skill sets are completely different.

“She has had an awful lot to learn in a very short space of time, and she has had a rough ride. If you take the route of being an MP and engaging with departments, there is a lot of stuff you absorb as you come up the tree.

“She hasn’t had the benefit of that.”

But for all her difficulties, Altmann remains supremely knowledgeable when it comes to pensions.

And it would look bad for the Government to evict her from the role, having only recruited a consumer champion in such a high-profile manner so recently.

As one source puts it: “Ros just being in the House of Lords could make life even more difficult for the Government.”